Propylene is an important organic chemical raw material. With the rapid increase of the demand for the derivatives such as polypropylene, the requirement for propylene in the whole world is increased rapidly year by year. Fluid catalytic cracking is one of the most important technologies to produce light olefins and propylene. As for most of the FCC apparatus, using the catalyst or the addition agent containing zeolite with MFI structure is an effective technology in order to increase light olefins and propylene.
U.S. Pat. No. 3,758,403 disclosed earlier that the method by adding ZSM-5 zeolite in the FCC catalyst might increase the octane number of gasoline and the yield of C3˜C4 olefins. For instance, when adding 1.5, 2.5, 5 and 10% ZSM-5 zeolite to the conventional catalyst with 10% REY molecular sieve, the octane number of gasoline is increased and the yield of low-carbon olefin is increased. The same result could be obtained by using the addition agent with ZSM-5 zeolite.
U.S. Pat. No. 5,318,696 disclosed a hydrocarbon conversion technology based on a catalyst which is consisted of a macroporous zeolite and a zeolite with MFI structure and a Si/Al ratio of lower than 30. This technology is used to produce gasoline with high octane number by employing improved FCC process and increase low-carbon olefins, especially propylene.
U.S. Pat. No. 5,997,728 disclosed a method in which a shape-selective cracking addition agent is used in large amount in the FCC process of heavy feedstock. The addition agent comprises the amorphous matrix by adding 12˜40% ZSM-5 zeolite, and its inventory in the system is at least 10%, which makes the content of ZSM-5 zeolite in the catalyst higher than 3%. This method increases low-carbon olefins in a large scale, at the same time it doesn't increase the yield of aromatic extraly and lose the yield of gasoline.
The cracking activity and hydrothermal stability of ZSM-5 zeolite is increased and the use level of zeolite can be reduced after the modification of ZSM-5 zeolite by phosphorus compounds.
CN1049406C disclosed a zeolite with MFI structure which containing P and rare earth. The anhydrous chemical expression is aRE2O3.bNa2O.Al2O3.cP2O5.dSiO2, in which a=0.01˜0.25, b=0.005˜0.02, c=0.2˜1.0 and d=35˜120. This zeolite displays excellent hydrothermal stability and good selectivity of low-carbon olefins when used in the conversion of hydrocarbons at high temperature.
CN1034223C disclosed a cracking catalyst used to produce low-carbon olefins, which is consisted of 0˜70% clay (based on weight of catalyst), 5˜99% inorganic oxide and 1˜50% zeolite. The zeolite is the mixture of 0˜25 wt % REY or high silica Y zeolite and 75˜100 wt % five membered ring high silica zeolite containing P and rare earth. The catalyst has higher hydrothermal activity and stability, conversion and yield of C2═˜C4═ than the catalyst using conventional ZSM-5 zeolite as active component.
U.S. Pat. No. 5,110,776 disclosed the preparation of ZSM-5 zeolite catalyst modified with P, in which the modification procedure with P is proceeded by dispersing the zeolite into a solution of P compounds at a pH value of 2˜6, mixing with matrix and spray-drying. The obtained catalyst increases the octane number of gasoline, and at the same time it doesn't increase the yield of dry gas and coke.
U.S. Pat. No. 6,566,293 disclosed a cracking catalyst comprising P modified ZSM-5 zeolite. The preparation of P modified ZSM-5 zeolite is proceeded by dispersing the zeolite into a solution of P compounds at a pH value of higher than 4.5, in which the loading content of P (calculated by P2O5) is at least 10 wt %, then mixing with matrix and other zeolite components and spray-drying. The obtained catalyst has high yield of low-carbon olefins.
U.S. Pat. No. 5,171,921 disclosed a ZSM-5 zeolite modified by P. The Si/Al ratio of the zeolite is 20˜60. After the immersion with P compounds and steam-aging treatment at 500˜700° C., the zeolite displays higher activity than the zeolite without P modification when used in the conversion of C3˜C20 hydrocarbons to C2˜C5 olefins.
U.S. Pat. No. 6,080,303 disclosed a method used to increase the catalytic activity of microporous and mesoporous zeolites, in which microporous and mesoporous zeolites are treated with P compounds firstly and then combined with AlPO4 gel. This method may improve the activity and hydrothermal stability of microporous and mesoporous zeolites.
U.S. Pat. No. 5,472,594 disclosed a hydrocarbon conversion technology based on a catalyst which comprises a macroporous zeolite and a P modified mesoporous zeolite with MFI structure. This technology is used to produce gasoline with high octane number by employing improved FCC process and increase low-carbon olefins, especially C4/C5.
Besides the P modification of ZSM-5 zeolite, the selectivity of the catalyst and addition agent for low-carbon olefins also could be improved by the introduction of P compounds to matrix.
USP2002/0003103A1 disclosed a FCC technology employed to increase the yield of propylene, in which at least part of the gasoline products are piped into the second riser reactor and cracked again. Besides macroporous zeolite such as USY, the catalyst composition used comprises mesoporous zeolite such as ZSM-5 and inorganic binder possessing cracking activity. The inorganic binder component contains P and the P/Al ratio is 0.1˜10. This technology may increase low-carbon olefins in a large scale, especially the yield of propylene.
USP2002/0049133A1 disclosed a catalyst with high zeolite content and high attrition strength. The catalyst comprises 30˜85 wt % ZSM-5 zeolite, 6˜24 wt % P (calculated by P2O5), <10 wt % Al2O3 and the remainder clay, in which P exists in matrix. When used in FCC process, the catalyst can increase light olefins, especially the yield of propylene.
The method of modifying zeolite with metal and its application were reported in following patents. For instance, U.S. Pat. No. 5,236,880 disclosed a catalyst containing the zeolites with MFI or MEL structures, in which the zeolite is modified by the metal of Group VIII, preferred by Ni. After the introduction of Ni, the zeolite is treated at a controlled temperature under thermal or hydrothermal conditions, which leads to the enrichment of the metal of Group VIII and Al on the surface. When used in the conversion of hydrocarbons, the catalyst may increase the octane number of gasoline and the yield of C3˜C4 olefins.
CN1057408A disclosed a cracking catalyst containing high Si zeolite and high cracking activity, in which the high Si zeolite is ZSM-5 zeolite, β zeolite or MOR zeolite containing 0.01˜3.0 wt % P, 0.01˜1.0 wt % Fe or 0.01˜10 wt % Al. The high Si zeolite is obtained by heating H- or K-ZSM-5 zeolite, β zeolite or MOR zeolite with a Si/Al ratio of higher than 15 to 350˜820° C. and passing it into an aqueous solution of Al halide, Fe halide or ammonium phosphate at a volume hourly space velocity of 0.1˜10 h−1.
CN1465527A disclosed a MFI zeolite with P and transition metal. The anhydrous chemical expression of the zeolite, calculated by mass of oxide, is (0˜0.3) Na2O.(0.5˜5) Al2O3.(1.3˜10) P2O5.(0.7˜15) M2O3.(70˜97) SiO2, in which M is selected from one of the transition metals Fe, Co and Ni. When used in the FCC procedure of petroleum hydrocarbon, the zeolite may increase the yield and selectivity for C2˜C4 olefins and result in higher yield of LPG.
At present for most of the FCC apparatus, increasing the concentration of propylene in LPG is an important way to increase the economic benefits for FCC apparatus at the same yield of LPG. Although the zeolite materials and catalysts disclosed in the prior art could effectively increase the yield of low-carbon olefins and the octane number of FCC gasoline products when used in FCC process, during the FCC reaction they give out relative low selectivity for propylene, so the scope for increasing propylene concentration in LPG is limited.